In order to meet the demand for wireless data traffic which has increased since the commercialization of a fourth Generation (4G) communication system, efforts have been made to develop an improved fifth Generation (5G) communication system or a pre-5G communication system. For this reason, the 5G or pre-5G communication system is called a “beyond 4G network communication system” or a “post Long-Term Evolution (LTE) communication system”.
In order to achieve a high data transfer rate, the 5G communication system is considered to be implemented in an ultra-high frequency (millimeter Wave (mmWave)) band (e.g., 60 GHz band). In order to reduce the path loss of radio waves and increase the transmission distance thereof in the mmWave band, techniques, such as beamforming, massive Multiple-Input Multiple-Output (MIMO), Full-Dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large scale antenna, are under discussion in the 5G communication system.
Also, in order to improve a network of a system, the development of techniques, such as evolved small cell, advanced small cell, cloud Radio Access Network (cloud RAN), ultra-dense network, Device-to-Device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), and reception interference cancellation, has been conducted in the 5G communication system.
In addition, hybrid Frequency Shift Keying (FSK) and Quadrature Amplitude Modulation (QAM) modulation (FQAM) and Sliding Window Superposition Coding (SWSC), which are Advanced Coding Modulation (ACM) schemes; and Filter Bank Multi-Carrier (FBMC), Non-Orthogonal Multiple Access (NOMA), and Sparse Code Multiple Access (SCMA), which are advanced access techniques, have been developed in the 5G system.
In an LTE system, a base station may transmit a Reference Signal (RS) referred to as a “Channel State Information (CSI)-Reference Signal (RS)”, and a user equipment may receive the CSI-RS and may calculate CSI, which is to be reported to the base station, by using the received CSI-RS.
FIG. 1 is a view for explaining a pattern of a CSI-RS defined in the LTE standards according to the number of ports.
(a) of FIG. 1 illustrates 20 CSI-RS patterns in a case where the number of CSI-RS ports is 2.
(b) of FIG. 1 illustrates 10 CSI-RS patterns in a case where the number of CSI-RS ports is 4.
(c) of FIG. 1 illustrates 5 CSI-RS patterns in a case where the number of CSI-RS ports is 8.
Table 1 below shows an example of CSI-RS configuration according to the number of CSI-RSs (i.e., the number of CSI-RS ports) which is configured.
TABLE 1CSI referenceNumber of CSI reference signals configuredsignal1 or 248configuration(k′, l′)ns mod 2(k′, l′)ns mod 2(k′, l′)ns mod 2Frame0(9, 5)0(9, 5)0(9, 5)0structure1(11, 2) 1(11, 2) 1(11, 2) 1type 12(9, 2)1(9, 2)1(9, 2)1and 23(7, 2)1(7, 2)1(7, 2)14(9, 5)1(9, 5)1(9, 5)15(8, 5)0(8, 5)06(10, 2) 1(10, 2) 17(8, 2)1(8, 2)18(6, 2)1(6, 2)19(8, 5)1(8, 5)110(3, 5)011(2, 5)012(5, 2)113(4, 2)114(3, 2)115(2, 2)116(1, 2)117(0, 2)118(3, 5)119(2, 5)1
With reference to FIG. 1 and Table 1, it can be noted that, when the number of CSI-RS ports is 1 (or 2), 4, and 8, there exist 20, 10, and 5 CSI-RS patterns (CSI-RS reuse patterns), respectively.
A CSI-RS reuse pattern is transmitted from a base station to a user equipment through a Radio Resource Control (RRC) message at long periods (e.g., a period of a few hundred milliseconds). By using the CSI-RS, the user equipment may estimate a Rank Indicator (RI), a Channel Quality Indicator (CQI), and a Precoding Matrix Indicator (PMI), and may feed back the estimated RI, CQI, and PMI to the base station.
Meanwhile, after Rel-13 of the LTE standard, according to the introduction of the concept of Full Dimension multiple-Input Multiple-Output (FD-MIMO) which considers the elevation angle of beamforming, the transmission of a BeamFormed CSI-RS (hereinafter, “BF-CSI-RS”) has been considered.